Conventionally, there is an optical print head in which two rows of light emitting elements are arranged in parallel below a rod lens array in which two rows of rod lenses arranged in parallel are integrated. The two rows of the light emitting elements are positioned alternately in an extending direction of the light emitting element rows.
In the optical print head, there is a case in which undesirable dispersion of light of each light emitted through the rod lens array by each light emitting element occurs. As the main reason of the dispersion, there is dispersion of luminous efficiency of each light emitting element and dispersion of a drive circuit connected with each light emitting element. As the main reason of the dispersion, there is dispersion of the refractive index distribution of the rod lens array and dispersion of a positional relation of each light emitting element with respect to each of the rod lens.
In a case of incorporating the optical print head in an image forming apparatus, the light emitted by each light emitting element forms a beam spot corresponding to one dot on a photoconductor. If there is dispersion of light of each light emitting element, density unevenness of an image occurs and the image quality is degraded. Thus, at the time of shipping the optical print head or at the time of shipping the image forming apparatus incorporated with the optical print head, a light amount correction operation for reducing the dispersion of the light is executed in manufacturing lines.
The amount of light dispersed by the light emitting element depends on an applied current value and light emitting time. In light amount correction, first, currents with the same value are applied to each light emitting element, and the light amount of each light emitting element (light amount of each light emitted through the rod lens array by each light emitting element) is measured. Next, under the condition of the application of the currents with the same value, the light emitting time of each light emitting element is adjusted with a PWM (Pulse Width Modulation) control so that the amounts of the light of the light emitting elements become identical. Correction information serving as an adjustment amount of the light emitting time of each light emitting element is information unique to the optical print head.
In the light amount correction, next, the correction information is written into a built-in memory of the optical print head. Through reading the correction information from the optical print head, the dispersion of the light of each light emitting element can be suppressed.
Incidentally, if the incorporation position of the light emitting element rows and the rod lens array deviates from an ideal position, a difference occurs in light transmittance. Thus, there is a case in which the amounts of light from the light emitting element rows are greatly different. If the amounts of light from the light emitting element rows are greatly different, there is a problem that the dispersion of the light cannot be completely suppressed through the light amount correction according to the light emitting time.